The future of carp control
Echo Lake near Hutchinson is small and shallow; a perfect place to catch carp. A boat with four researchers has set out hoping to sneak up on some carp and catch them for study. But there's no fishing pole or lures here.
The boat moves toward some overhanging trees along the shady lakeshore. A few seconds later dozens of fish float to the surface. They've been stunned by a generator that sends a pulse of electricity into the water. Paralyzed carp bob on the water before they're snagged with nets.
A researcher measures the greenish-yellow fish. They're two feet and longer and as big around as a log. Their thick skin and heavy scales make them look positively prehistoric.
The carp are implanted with a numbered tag and thrown back into the lake where they quickly recover from the experience and swim away.
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Researchers hope to catch some of these fish again in coming years as a part of a project to track their life cycle.
In other parts of the world, in Asia and Europe for example, carp are seen as an abundant source of food. They were brought to the U.S. in the 1800s for the same purpose.
But they're an invasive species that, in the last 100 years, has spread across the country. They can take over a lake, competing for food with native species, or just by eating the young of other fish.
And they're not much better for the health of the lake. According to University of Minnesota biologist Peter Sorenson, bottom-feeding carp can stir up nutrients, destroy aquatic plants and muddy the water. That's bad for other fish and waterfowl.
"They can cause great harm to shallow lakes and wetlands, they're probably one of the bigger threats facing many of the shallow lakes and Minnesota and elsewhere in the Midwest," Sorenson said.
For that reason, people have worked for decades to come up with a way to get rid of carp. But Sorenson thinks they skipped a step, they don't know their enemy.
"People have been so obsessed with trying to get them out of the system and kill them, they really haven't just sat down for a minute to try and figure out their basic biology, what makes them tick," Sorenson said.
Sorenson also wants to figure out how to get rid of carp, or at least control them, but first he wants to learn as much about carp as possible. He's just begun a four year long project that seeks to discover what biologists don't know about carp, which is a lot.
"We don't know how many there are, we don't know at what age they reproduce or how many young they have or where they go. If you're looking for a solution that's a little more complicated than just poisoning the entire system, you've got to know these things, and we're going to find it out," Sorenson said.
Then Sorenson hopes biologists can finally come up with a plan to keep carp from taking over waterways. He's already has a few ideas, like using pheromones to attract and capture carp, or stocking extra sunfish in a lake to eat baby carp.
"Every lake system in Minnesota is different, every one is going to need a slightly different solution. But what people need are tools to evaluate this and that's really the objective of this project. It's only four years long but to be honest it's going to take a while to figure this out, but I think we can do it," Sorenson said.
An effective way to get rid of carp is something lake associations and fisheries biologists can't wait to get their hands on. But Sorenson warns a carp control plan that's backed by solid science will take time.